FIGS. 18 to 20 are sectional views of the main portion of a conventional scroll-type compressor of a first type disclosed for example in Japanese Patent Laid-Open No. 59-120794, in which 1 is a stationary scroll, 2 is an orbiting scroll defining a compression chamber together with the stationary scroll 1, 23 is a thrust surface of the orbiting scroll 2 at the side opposite to the compression chamber, 24 is an orbiting shaft disposed at the center of the thrust surface 23, 3 is a frame journaling the thrust surface 23 of the orbiting scroll 2, 5 is a main shaft for transmitting a drive force to the orbiting scroll 2, 27 is a motor for driving the main shaft 5, 7 is a slider rotatably accommodated within the orbiting bearing, 31 is a point of contact at which the stationary scroll 1 and the orbiting scroll 2 contact, 8 is a discharge valve disposed at a position for discharging the refrigerant, 21a is a load direction surface of a slider sliding surface and 21b is a non-load direction surface of the slider sliding surface.
The operation will now be described. The drive force of the motor 27 is transmitted to the main shaft 5, the slider 7 is rotated by the rotation of the main shaft 5 while maintaining a constant revolution radius r and is slidable along the contact surface between the slider 7 and the main shaft 5, so that the rotation of the slider 7 causes the orbiting scroll 2 to repeat orbiting motion at a constant revolution radius r, whereby a volume defined between the stationary scroll 1 and the orbiting scroll 2 decreases to compress the refrigerant which is then discharged from the discharge valve 8. The discharge valve 8 also functions as a check valve.
In FIG. 19, a resultant force F of a centrifugal force Fc on the slider 7 and a gas load force Fg generated by the compression acts on the slider 7, so that the slider 7 is moved along the sliding surface 21 in the direction along which the revolution radius is increased to urge the orbiting scroll 2 against the stationary scroll 1, whereby no clearance is generated at the point of contact 31 between the orbiting scroll 2 and the stationary scroll 1 and a compression with only a small leakage can be achieved.
FIG. 21 is a longitudinal sectional view illustrating the conventional scroll-type compressor of the second type disclosed in Japanese Patent Application No. 2-29127 filed previously by the applicant of the present application and FIG. 22 is a sectional view of the main portion of the structure shown in FIG. 21 and illustrating forces acting upon the main portion during the motor forward rotation. In FIG. 21, 1 is a stationary scroll, 2 is an orbiting scroll, 2a is a base plate for the orbiting scroll 2, 2b is an orbiting bearing disposed on the base plate 2a at the center of the non-compression chamber side, 3 is a frame fixed to the stationary scroll 1 by means of a bolt or the like, 4 is a ring-shaped Oldham's ring for preventing spinning of the orbiting scroll 1 and for connecting it to the frame 3 for the revolution movement in the radial direction, 5 is a main shaft having formed at its top end an eccentric slider mounting shaft 6 having a flat surface 6a and a flat surface 6b parallel to the axis of the main shaft 5, the slider mounting shaft 6 having mounted thereon a slider 7 so that it is not rotatable but slidable along a plane perpendicular to the axis of the main shaft 5 and it is fitted by the orbiting bearing 2b in an eccentric state relative to the axis of the main shaft 5. 8 is a discharge valve which also functions as a check valve.
Also, in FIG. 22, 7a is a fitting hole formed in the slider 7 for receiving the slider mounting shaft 6 wherein, 7b is a sliding surface of the slider 7 and 7c is an opposite sliding surface r is an eccentricity amount or a distance between the axis of the main shaft 5 (the center of the stationary scroll 1) and the axis of the orbiting bearing 2b (the center of the orbiting scroll 2 and also the center of the slider 7), and r.sub.1 is an eccentricity amount when the scroll of the orbiting scroll 2 is in contact in radial direction with the scroll of the stationary scroll 1. Fca is a centrifugal force of the orbiting scroll 2 and the slider 7 generated when the orbiting scroll 2 is in the revolution movement, which acts along the line connecting the center of the main shaft 5 and the center of the slider 7, Fga is a compression load acting on the orbiting scroll 2 in the direction perpendicular to the centrifugal force Fca, Fra is an compression load acting on the orbiting scroll 2 in the direction opposite to the centrifugal force Fca, Fna and .mu. a are contact force and coefficient of friction between the sliding surface 7b of the slider 7 and the flat surface 6a of the slider mounting shaft 6. .alpha. is an angle defined between the sliding direction of the slider 7 and Fca or the direction of eccentricity, Which is shifted in the direction opposite to the direction Of rotation of the main shaft 5 relative to the direction of Fca and which is referred to as an inclination angle. Here, the sliding direction of the slider 7 refers to the direction of movement of the slider 7 for increasing the the eccentricity amount r or the direction of movement direction for urging the scrolls. Basically, the centrifugal force Fca acts on the center of the gravity, and Fga and Fra act on the midpoint between the axes of the main shaft 5 and the orbiting bearing 2b. However, the moment due to the positional displacement of these forces is restricted by the Oldham's ring 4 and the reaction from the Oldham's ring 4 is made not to be introduced into this system, so that these forces are deemed to act on the axis of the orbiting bearing 2b or the center of the slider 7.
The operation will now be described. When the power source terminals are correctly connected and the motor and the main shaft 5 are rotated in forward direction, the orbiting scroll 2 makes a revolution motion about the axis of the main shaft 5 as it is being guided by the Oldham's ring 4, decreasing the volume of the compression chamber defined between the coupled scrolls 2 and 1, whereby the refrigerant is compressed and discharged from the central compression chamber through the discharge valve 8.
During the forward rotation, as illustrated in FIG. 22, the sliding-direction component of the resultant force of the centrifugal force Fca and the compression loads Fga, Fra is greater than the frictional force .mu. aFna (which varies in direction by 180.degree. according to the direction of movement of the slider 7) between the sliding surface 7b of the slider 7 and the flat surface 6a of the slider mounting shaft 6, so that EQU .mu.aFna&lt;(Fca-Fra) cos .alpha.+Fga sin .alpha.. . . (1)
is satisfied, and the slider 7 is displaced in sliding direction to the position at which the orbiting scroll 2 is brought into contact with the stationary scroll 1 or to the eccentricity amount r.sub.1 which is determined by both the scrolls to urge the orbiting scroll 2 against the stationary scroll 1, whereby the clearance or gap in the radial direction between the scrolls is made zero and the compression can be achieved. Also, since the slider 7 is slidable along the sliding direction in either direction beyond the state where it is moved to the eccentricity amount r.sub.1, it can slide until both of the scrolls are brought into contact even when the configuration of the scrolls of the stationary scroll 1 and the orbiting scrolls is different from the predetermined one complete dimensions, the radial clearance during revolution can be always maintained at zero.
Also, when the motor and the main shaft 5 rotate in the reverse direction by, for example, the incorrect connection of the power source terminals, forces illustrated in FIG. 23 are generated. During the reverse rotation, the volume of the compression chamber increases, so that the pressure within the central compression chamber decreases and the discharge valve 8 is closed to function as a check valve, whereupon no refrigerant flows in the reverse direction.
Therefore, the suction pressure (the balanced pressure before the operation) outside of the compression chamber becomes higher than the pressure within the compression chamber which has increasing inner volume, so that the directions of the compression loads Fgb and Fra shift by 180.degree. relative to those obtained during the forward rotation. In FIG. 23, although the inclination angle a is formed in the direction of rotation of the main shaft 5, its amount does not change as compared to that obtained during the forward rotation, or when only an angle corresponding to a small clearance necessary for fitting of the slider mounting shaft 6 into the slider fitting hole 7a is added to the inclination angle .alpha., EQU (Fca+Frb) cos.alpha.-.mu.bFnb&gt;Fgb sin .alpha.. . . (2)
Fcb: centrifugal force upon reverse rotation (Fcb =Fca) PA1 Fgb: compression load acting perpendicular to centrifugal force Fcb upon reverse rotation PA1 Frb: compression load acting oppositely to centrifugal force Fcb upon reverse rotation PA1 Fnb, .mu.b: contacting force and frictional coefficient between opposite sliding surface 7c and flat surface 6b, respectively stands, wherein the slider 7 moves in the sliding direction similarly in the forward rotation state to urge the orbiting scroll 2 against the stationary scroll 1, making the radial clearance zero and rotating in the reverse direction.
FIG. 24 shows a conventional scroll-type compressor of the third type add FIGS. 25 and 26 are detailed views of the related parts of a gear pump 9.
A pump case 9a has in its lower half a space containing an inner gear 9b having formed gear teeth in the outer side surface and an outer gear 9c having gear teeth engaging the teeth of the inner gear 9b formed in the outer side surface, and the pump case 9a has in its upper half a bore for allowing a pump drive portion 5d disposed at the lower end of the main shaft 5 to extend there through.
The gaps defined between the inner gear 9b and the outer gear 9c are generally separated by gear teeth into three gap spaces, i.e. a gap space 9h, a gap space 9i and a gap space 9j, which successively shift in the direction of rotation upon the rotation of the gears.
A pump port 9d is provided with an oil suction port 9e and an oil discharge port 9f and an oil suction pipe 9g is attached in communication to the lower through hole of the oil suction port 9e. The gap space 9h is in communication with the oil suction port 9e, the gap space 9j is in communication with the oil discharge port 9f and the gap space 9i is not communicated with any of the ports. The pump case 9a and the pump port 9d are securely accommodated within a sub-frame 11.
In FIGS. 24 to 26, the forward rotation (counterclockwise rotation in FIG. 26) of the main shaft 5 causes the inner gear 9b to be driven in the counterclockwise direction, and the outer gear 9c in mesh with the inner gear 9b through the gear teeth is also driven in the counterclockwise direction. By the counterclockwise rotation of these gears, the gap space 9h out of three gap spaces defined between the gears is increased in its inner volume, while the gap space 9i is at its maximum and the gap space 9j is decreased in its inner volume. Therefore, the lubricating oil staying at the bottom of the hermetic vessel 10 is suctioned into the volume-increasing gap space 9h through the oil suction pipe 9g and the oil suction port 9e. The lubricating oil is then supplied through the gap space 9i to the volume-decreasing gap space 9j. The lubricating oil is further discharged to the oil discharge port 9f due to the decrease of the inner volume of the gap space 9j and then supplied to each sliding portion of the compressor through the oil passage hole formed in the center of the main shaft 5.
Since the previously-described conventional scroll-type compressor of the first type is constructed as previously described, even when the compressor is reversely rotated by the incorrect connection of the power source terminals for example, the discharge valve prevents the reverse flow of the refrigerant and the slider moves in the direction in which the radius of revolution increases because of the resultant force F of the centrifugal force Fc and the gas load Fg shown in FIG. 20, so that there is no refrigerant leakage and the stationary scroll and the orbiting scroll compress the refrigerant only within the compression chamber to purge the refrigerant on the suction port side to make the compression chamber in a vacuum state. Therefore, the stationary scroll and the orbiting scroll are deformed and the teeth tips and the teeth bases are brought into abnormal contact, disadvantageously resulting in the damages of the addendum of the stationary scroll and the orbiting scroll.
In the conventional scroll-type compressor of the second type, in the event that the motor makes a reverse rotation due to the incorrect connection of the power terminals for example, the inner volume of the compression chamber increases with the radial clearance between the scrolls is zero and the discharge valve functions as a check valve which prevents the reverse flow of the refrigerant, the compression chambers less the most outside chamber is brought into a vacuum state after a continued reverse rotation to make a large axial deformation of the stationary scroll and the orbiting scroll which causes an abnormal contact between the teeth tips and the bases of the scrolls and damages in the addendum, resulting in an inoperable condition.
If the inclination angle .alpha. is made large, a relationship EQU (Fcb+Frb) cos.alpha.+.mu.bFnb&lt;Fgb sin.alpha.. . . (3)
is established upon the reverse rotation, and the slider moves in the direction in which the eccentricity r of the orbiting scroll decreases and a radial clearance is formed between the scrolls whereby the vacuum condition can be relieved therethrough. However, upon the forward rotation, with the large inclination angle .alpha., since the slider is moved in the sliding direction by a large force in accordance with the equation (1), the contacting force by which the scroll member of the orbiting scroll is Urged against the scroll member of the stationary scroll is increased and the friction therebetween causes the increase of mechanical loss, whereby the performance of the compressor is significantly degraded and, in the worst case, the scroll member of the stationary and orbiting scrolls are destroyed by the urging, contacting force.
As for the oil supply in the conventional scroll-type compressor of the third type, since the inner gear 9b and the outer gear 9c are driven in the clockwise direction in FIG. 25 during the reverse rotation, the volume of the previously discussed gap space 9j increases and the volume of the gap space 9h decreases. Therefore, the lubricating oil is introduced from the oil discharge port 9f communicated to the main shaft 5 into the oil suction port 9e communicated to the hermetic vessel 10 and the gear pump 11 fails: to achieve the function of supplying the lubricating oil staying at the bottom of the hermetic vessel 10 to each sliding portion of the compressor, whereby the sliding portion are disadvantageously run out of the lubricating oil and results in seizure of the sliding portion.